 /*******************************************************************************
  * Copyright (c) 2005, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/

 package org.eclipse.ui.internal.expressions;

 import org.eclipse.core.expressions.EvaluationResult;
 import org.eclipse.core.expressions.Expression;
 import org.eclipse.core.expressions.ExpressionInfo;
 import org.eclipse.core.expressions.IEvaluationContext;
 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.jface.viewers.ISelection;
 import org.eclipse.ui.ISources;
 import org.eclipse.ui.IWorkbenchWindow;
 import org.eclipse.ui.SelectionEnabler;

 /**
  * <p>
  * An expression wrapper for the legacy {@link SelectionEnabler}. This emulates
  * an {@link Expression} using an instance of <code>SelectionEnabler</code>.
  * </p>
  * <p>
  * This class is not intended for use outside of the
  * <code>org.eclipse.ui.workbench</code> plug-in.
  * </p>
  *
  * @since 3.2
  */
 public final class LegacySelectionEnablerWrapper extends
         WorkbenchWindowExpression {

     /**
      * The seed for the hash code for all schemes.
      */
     private static final int HASH_INITIAL = LegacySelectionEnablerWrapper.class
             .getName().hashCode();

     /**
      * The enabler for this expression; never <code>null</code>.
      */
     private final SelectionEnabler enabler;

     /**
      * Constructs a new instance of <code>SelectionEnablerExpression</code>.
      *
      * @param enabler
      * The enabler; must not be <code>null</code>.
      * @param window
      * The workbench window which must be active for this expression
      * to evaluate to <code>true</code>; may be <code>null</code>
      * if the window should be disregarded.
      */
     public LegacySelectionEnablerWrapper(final SelectionEnabler enabler,
             final IWorkbenchWindow window) {
         super(window);

         if (enabler == null) {
             throw new NullPointerException ("There is no enabler"); //$NON-NLS-1$
 }
         this.enabler = enabler;
     }

     public final void collectExpressionInfo(final ExpressionInfo info) {
         super.collectExpressionInfo(info);
         info.markDefaultVariableAccessed();
     }

     protected final int computeHashCode() {
         int hashCode = HASH_INITIAL * HASH_FACTOR + hashCode(getWindow());
         hashCode = hashCode * HASH_FACTOR + hashCode(enabler);
         return hashCode;
     }

     public final boolean equals(final Object object) {
         if (object instanceof LegacySelectionEnablerWrapper) {
             final LegacySelectionEnablerWrapper that = (LegacySelectionEnablerWrapper) object;
             return equals(this.enabler, that.enabler)
                     && equals(this.getWindow(), that.getWindow());
         }

         return false;
     }

     public final EvaluationResult evaluate(final IEvaluationContext context)
             throws CoreException {
         final EvaluationResult result = super.evaluate(context);
         if (result == EvaluationResult.FALSE) {
             return result;
         }

         final Object defaultVariable = context
                 .getVariable(ISources.ACTIVE_CURRENT_SELECTION_NAME);
         if (defaultVariable instanceof ISelection) {
             final ISelection selection = (ISelection) defaultVariable;
             if (enabler.isEnabledForSelection(selection)) {
                 return EvaluationResult.TRUE;
             }
         }

         return EvaluationResult.FALSE;
     }

     public final String toString() {
         final StringBuffer buffer = new StringBuffer ();
         buffer.append("LegacySelectionEnablerWrapper("); //$NON-NLS-1$
 buffer.append(enabler);
         buffer.append(',');
         buffer.append(getWindow());
         buffer.append(')');
         return buffer.toString();
     }
 }

